Menstrual periods are an unnecessary nuisance that could be eliminated from women's lives with little harm. That's the message starting to spread from specialists in reproductive medicine.

The latest evidence comes from the study of a new contraceptive pill that has been designed to be taken continuously, rather than with a break each month to trigger bleeding. The study showed that this pill appeared just as safe as others over the short term and that perhaps no surprise women suffered from fewer menstrual problems (from cramps to mood swings) each month.

The idea that women should have a monthly period is widely accepted but has little scientific rationale, according to some experts. Long before the arrival of contraception, fertile women would have been pregnant or breastfeeding during most of their reproductive lifespan, leaving only a few months between children for periods.

When the oral contraceptive was developed in the 1950s, doctors thought women would be reassured that they were fertile and not pregnant if their periods continued. So a typical pill, containing synthetic oestrogen and progesterone to suppress ovulation, is taken for three weeks followed by one week's break.

But for years some doctors have been telling certain women, including those with medical conditions that make periods intensely painful, that they can take the pill continuously. Some women make the decision for themselves.

Non-stop pill popping

The latest study is on a pill called Lybrel, and was paid for by Wyeth Pharmaceuticals, the company that has asked the US Food and Drug Administration to approve the pill. It contains levels of oestrogen very similar to those in existing contraceptive pills and a slightly lower dose of the progesterone.

The phase III study, of over 2,100 women, is the largest yet to look at the effects of halting periods using a pill. The researchers found that the pill is as effective a contraceptive as others, and side-effects ranging from headaches to changes in cholesterol levels were no worse over the study period of a year1. A second study, which has not yet been published, shows that the pill decreased some of the unpleasant symptoms women experience with their periods, says lead author David Archer at the Eastern Virginia Medical School, in Norfolk.

One downside of the new continuous-use pill is that around 40% of women still experienced unpredictable bleeding. Nearly 60% of women in the study chose to stop taking the pills before the year was up.

Give me a break

"In women taking contraception there is no real need for periods at all," says Freedolph Anderson, who has studied continuous-use oral contraceptives at the Eastern Virginia Medical School. "Doctors have known this for a long time."

But researchers do not yet know whether contraceptive pills taken without a break generate increased risks of problems after many years (the longest studies, like this one, last about a year). The pill is thought to increase the risk of blood clots and heart attacks in some women and there is still debate about whether it raises the risk of breast cancer. On the flip side, it is linked to lower risks of ovarian and endometrial cancer.

Specialists say that the doses of hormones in Lybrel are relatively low and so are unlikely to add up to increased risks. "I don't see any immediate downside of taking 90 more pills a year," says Archer. Even so, long-term studies of this type have not been done and any increased risks could take decades to emerge.

That time of the year

In the meantime, several options are opening for women who have a medical reason or just a desire to eliminate the pain and hassle of periods.

Seasonale, which was introduced in the United States in 2003, is one drug that produces only four periods per year. Others contraceptives, such as injections of a synthetic progesterone, can sometimes stop periods completely.

Linda Miller, who studies menstrual suppression at the University of Seattle, Washington, argues that women would do as well or better simply taking their regular contraceptive pill without a break, rather than switching to a custom-designed continuous-use contraceptive. She notes that there is a financial incentive to develop pills such as Lybrel, as companies can get patent protection and exclusive marketing for such products.